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                                                                    Exhibit 3.21
                          CERTIFICATE OF INCORPORATION

                                       OF

                              GIANT YORKTOWN, INC.

      1. The name of the Corporation is Giant Yorktown, Inc. (the
"Corporation").

      2. The address of the registered office of the Corporation in the State of
Delaware is Corporation Trust Center, 1209 Orange Street, in the City of
Wilmington, County of New Castle. The name of its registered agent at that
address is The Corporation Trust Company.

      3. The purpose of the Corporation is to engage in any lawful act or
activity for which corporations may be organized under the General Corporation
Law of the State of Delaware (the "DGCL").

      4. The total number of shares which the Corporation will have authority to
issue is 500,000 shares of common stock, par value $ 1.00 per share.

      5. The name and mailing address of the incorporator is Kim H. Bullerdick
at 23733 N. Scottsdale Road, Scottsdale, Arizona 85255.

      The powers of the incorporator shall terminate upon the filing of this
Certificate of Incorporation.

      6. The initial Directors of the Corporation and their addresses are as
follows:

                         James E. Acridge
                         Fredric L. Holliger
                         Morgan M. Gust
                         23733 N. Scottsdale Road
                         Scottsdale, Arizona 85255

      7. In furtherance and not in limitation of the powers conferred by
statute, the Board of Directors shall have the power to make, alter, amend,
change, add to or repeal the bylaws of the Corporation.

      8. Elections of directors need not be by written ballot unless the bylaws
of the Corporation shall so provide.

      9. The Corporation reserves the right to amend, alter, change or repeal
any provision contained in this Certificate of Incorporation, in the manner now
or hereafter prescribed by statute.

      10. A director of the Corporation shall not be personally liable to the
corporation or its stockholders for monetary damages for breach of fiduciary
duty as a director, except to the extent that the elimination or limitation of
liability is prohibited under the DGCL as in effect when such
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liability is determined. No amendment or repeal of this provision shall deprive
a director of the benefits hereof with respect to any act or omission occurring
prior to such amendment or repeal.

      11. The Corporation shall, to the fullest extent permitted by Section 145
of the DGCL, as amended from time to time, or any successor section, indemnify
each person who was or is a party or is threatened to be made a party to any
threatened, pending or completed action, suit or proceeding, whether civil,
criminal, administrative or investigative, by reason of the fact that he is or
was a director or officer of the Corporation, or is or was serving at the
request of the Corporation, as a director, officer, employee or agent of another
corporation, partnership, joint venture, trust or other enterprise, against
expenses (including attorneys' fees), judgments, fines and amounts paid in
settlement actually and reasonably incurred by him in connection with such
action, suit or proceeding and any appeal therefrom.

      Indemnification may include payment by the Corporation of expenses in
defending an action or proceeding in advance of the final disposition of such
action or proceeding upon receipt of an undertaking by the person indemnified to
repay such payment if it is ultimately determined that such person is not
entitled to indemnification under this Article, which undertaking may be
accepted without reference to the financial ability of such person to make such
repayments.

      The Corporation shall not indemnify any such person seeking
indemnification in connection with a proceeding (or part thereof) initiated by
such person unless the initiation thereof was approved by the Board of Directors
of the Corporation.

      The indemnification rights provided in this Article 11 (i) shall not be
deemed exclusive of any other rights to which those indemnified may be entitled
under any law, agreement or vote of stockholders or disinterested directors or
otherwise, and (ii) shall inure to the benefit of the heirs, executors and
administrators of such persons. The Corporation may, to the extent authorized
from time to time by its Board of Directors, grant indemnification rights to
other employees or agents of the Corporation or other persons serving the
Corporation and such rights may be equivalent to, or greater or less than, those
set forth in this Article 11.

      12. Whenever a compromise or arrangement is proposed between this
Corporation and its creditors or any class of them and/or between this
Corporation and its stockholders or any class of them, any court of equitable
jurisdiction within the State of Delaware may, on the application in a summary
way of the Corporation or of any creditor or stockholder thereof, or on the
application of any receiver or receivers appointed for this Corporation under
Section 291 of Title 8 of the Delaware Code or on the application of trustees in
dissolution or of any receiver or receivers appointed for this Corporation under
Section 279 of Title 8 of the Delaware Code order a meeting of the creditors
and/or class of creditors, and/or of the stockholders or class of stockholders
of this Corporation, as the case may be, to be summoned in such manner as the
said court directs. If a majority in number representing three-fourths in value
of the creditors or class of creditors, and/or of the stockholders or class of
stockholders of this Corporation, as the case may be, agree to any compromise or
arrangement and to any reorganization of this Corporation, as a consequence of
such compromise or arrangement, the said compromise or arrangement and the said
reorganization shall, if sanctioned by the court to which the said application
has been made, be binding on all the creditors or class of creditors, and/or on
all the stockholders or class of stockholders, of this Corporation, as the case


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may be, and also on this Corporation.

      13. Immediately after the filing of this Certificate of Incorporation with
the Delaware Secretary of State, the undersigned incorporator shall resign and
thereafter the affairs of the Corporation shall be managed by the directors
named herein and their successors.

      IN WITNESS WHEREOF, the undersigned incorporator has caused this
Certificate of Incorporation to be duly executed as of the 5th day of March,
2002.


                                        /s/ Kim H. Bullerdick
                                        ------------------------------------
                                        Kim H. Bullerdick, Incorporator


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